The ability to control propagation of electromagnetic radiation is important in many different technology areas, such as optical fiber systems and electronic devices. Devices for controlling propagation of electromagnetic radiation can form important components in many electronic and optical devices. For example, modulators are used in optical fiber systems for modulating an intensity of a carrier signal in order to generate an encoded signal. Modulators can also form important components in photonic integrated circuits (“PICs”) that include electronic devices and optoelectronic devices. PICs are the photonic equivalent of electronic integrated circuits and may be implemented on a semiconductor substrate that forms the base of the electronic and optoelectronic devices. As one example, a modulator can be used to modulate an optical signal that is communicated between different electronic devices or different functional circuitry on the same substrate.
Metamaterials appear to be a promising candidate for use as switches, modulators, and filters in electronic and optical devices. Metamaterials are materials that are engineered to have electromagnetic responses that can be impossible in naturally occurring materials, such as a negative refractive index. The refractive index of a material, n, is a measure of the speed of light in the material, and is given by n=√{square root over (μ·∈)}, where μ is the material's permeability to magnetic fields, and ∈ is the materials permittivity to electric fields. Most naturally occurring materials have positive μ and positive ∈. The refractive index is a real and positive number in such naturally occurring materials.
Assembling a collection of appropriately designed metallic structures enables fabricating a metamaterial that has a negative μ and/or a negative ∈ for incident electromagnetic radiation of a particular frequency. For example, an array of split-ring resonators (“SRRs”) is one type of electromagnetic resonator structure that has a negative μ and a cut-wire structure is a structure that has a negative ∈. A one-, two-, or three-dimensional arrangement of SRRs and cut-wires's may form an effective medium that exhibits a negative refractive index. Additionally, transmission through an array of SRRs or a cut-wire structure is substantially reduced at frequencies at and near a characteristic resonant frequency. Moreover, the transmission characteristics of a metamaterial can be designed by changing the size and configuration of the individual SRRs and wires. Accordingly, metamaterials may be designed for use with incident electromagnetic radiation over a wide range of frequencies.
Metamaterial's unique transmission characteristics makes them suitable for use in many types of optical and electronic devices as switches, modulators, or other components. However, there is still a need for improved metamaterial-based devices for use in many different types of electronic and optical devices.